We are studying the correlation of metabolic sequences with special emphasis on the role of the adenine nucleotides. Approaches include comparison of the effects of the adenylate energy charge and of the size of the adenine nucleotide pool on the activities of enzymes in vitro, the effect of limitation of activity of adenylate kinase in vivo (achieved with the use of a heat-sensitive mutant strain), the effect of the external ATP/ADP ratio on the activity of mitochondria in vitro, and the regulation of the enzymes involved in primary uptake of ammonia.